Conventional diaphragms include a paper layer and a coating layer. The paper layer is formed of cellulose fibers. The coating layer contains an inorganic material and a resin. The coating layer is laminated on the paper layer.
The paper layer of the conventional diaphragms is produced using a dispersion liquid obtained by dispersing cellulose fibers in water. First, the dispersion liquid is dewatered by papermaking to produce a cellulose fiber deposit. Next, the deposit is dried to form a paper layer for a diaphragm. Subsequently, onto the thus-formed paper layer, a mixed solution of an inorganic material and a resin is applied as a coating layer. Finally, the resultant is heated to cure the resin. Through the above-described steps, a diaphragm including a paper layer and a coating layer laminated on the paper layer can be manufactured (for example, see Patent Literature 1).